Removable coating compositions

ABSTRACT

A coating composition is described comprising a multi-stage emulsion polymer that is both radiation curable, removable and includes chemically reactive functional groups in the coating that react with one or more conventional chemical stripping agents, effecting the removal of the coating from a substrate. The UV curable and removable composition is included within one or more layers applied on top of a substrate or on top of a base coat that itself is disposed on top of a substrate.

[0001] The present invention relates to curable compositions included ina protective coating or within one or more coating layers that can bereadily removed after the coating is applied to a substrate. Inparticular, it is directed to a floor coating that is prepared viaradiation curing of a polymer, a floor coating including chemicallyreactive polymers or polymers having chemically reactive functionalgroups triggered to release the coating from a substrate, a floor finishsystem including removable radiation cured compositions, a process forapplying removable radiation cured coatings to a substrate, a subsequentprocess for chemically removing coatings from a substrate, amultifunctional polymer useful in the formulation of the removableradiation curable compositions and their method of preparation.

[0002] Conventional highly cross-linked coating compositions typicallydo not provide easily removable coatings using traditional strippingoperations (for example, treatment with solvent and ammonia or amines).Highly cross-linked coatings are desirable because of enhanceddurability characteristics (such as long wear and scuff resistance) andare typically based on two-component (reactive) systems or systemsrequiring external energy sources to induce cross-linking (UV, electronbeam) such that the resultant coatings do not swell significantly whenexposed to typical chemical swelling agents and the film integrity isnot disrupted to a sufficient extent to allow ready removability from asubstrate. It is desirable to provide floor coating compositions thatare applied to a substrate (e.g vinyl flooring, concrete) whichimmediately dry and cure in air during a single application and whichcan readily be removed after the coating is applied to the substrate. Ingeneral, the coating and finishes cannot be easily removed from theflooring to which they are applied using conventional chemical strippingcompositions in combination with a stripping pad or brush. Highlycross-linked UV cured polymer coatings and finishes applied tosubstrates such as concrete also cannot be removed using conventionalchemical floor stripping techniques. Typically, the coatings are removedby abrasive processes including sanding, which can result in irreparabledamage to the concrete surface.

[0003] U.S. Pat. No. 6,197,844 B1 discloses a curable coatingcomposition comprising (a) poly (isocyanurate) oligomer having at leastthree terminal reactive isocyano functional groups that can be reactedwith (b) hydroxy alkylacrylate and (c) tertiary amine alcohol in a molarratio of a:b:c of about 1:1.1-2.5:0.5-2, wherein b+c is at least 3 andno greater than the total amount of terminal reactive groups of (a).Curable coatings prepared from poly(isocyanurate) compositions, however,suffer a number of limitations and present safety, health andenvironmental problems. The isocyano functional groups are chemicallyreactive and inherently toxic to the user of such compounds. Thepoly(isocyanurate) compositions are difficult to store for long periodsof time; the isocyano functional groups readily react with water (i.e.in the form of moisture, humidity). The stripped materials arepotentially harmful to users during handling and have a negativeenvironmental impact on disposal. In addition, the stripped materialshave separate toxicity issues associated with their handling andremediation. Problems are likely encountered with mixing thepoly(isocyanurate) compositions with acrylic emulsion polymers,including incompatibility of the two components and the burden andinefficiency of additional steps. The poly(isocyanurate) material mayhave to be pre-emulsified before it can be added to the latex polymer.Improper pre-emulsification leads to defects in the final UV-curedcoating. Other problems have been noted in the formulation of UV curablefloor finish systems including an appearance of color in the hardenedcoating and/or an altered color of the coated substrate referred to asyellowing, noticeable odors of monomers during curing of the coating,and high levels of both photo-initiator and radiation source intensityrequired for producing the hardened coating.

[0004] Similarly, single-package cross-linkable coating formulationsbased on polyurethane type and other latent cross-linking mechanisms(such as multi-component systems) possess enhanced durabilitycharacteristics (scuff, mar or scratch resistance), but without theadvantage of being readily removable upon demand. Due to their inherentlack of easy removability these highly durable coatings are typicallylimited in use to factory applied coatings and special end user markets,for example high performance wood floor coatings and industrialmaintenance coatings.

[0005] It is desirable to provide coating compositions having theadvantages of both the enhanced durability of highly cross-linkedcoatings and the easy removability of the conventional less durable,coating compositions. A long felt and still unsolved need exists toprovide curable yet removable coatings suitable for use as a floorfinish that are easily applied to a floor substrate or that are includedwithin one or more coating layers on top of the substrate, that cure inair upon exposure to low intensity radiation without objectionableodors, that possess little or no toxicity during storage and handling bya user and that have minimal environmental impact when the cured coatingis stripped and disposed of, that provide a protective coating(s)substantially free of observable color and that include highlycross-linked compositions that are easily removed from the floor by asuitable chemical stripping composition. The problem addressed by thepresent invention is to provide coating compositions having thesecombined advantages, previously unavailable in conventional coatingcompositions. Inventors have discovered that radiation curable emulsionpolymer compositions including one or more multifunctional monomers inat least one stage of the polymer have significant utility as radiationcured yet removable coatings. Finishes including the removable radiationcurable compositions can be cured rapidly when exposed to low intensityUV radiation to provide durable, protective coatings on a substrate.Functional groups in the coating can be chemically activated to effectthe rapid removal of the. coating when exposed to conventional chemicalstripping agents.

[0006] Accordingly, there is provided a multifunctional polymer usefulin the formulation of removable radiation curable compositions, thepolymer comprising (a) a plurality ethylenically unsaturated groups and(b) a plurality of chemically reactive functional groups; that forms ahighly cross-linked coating on a substrate or within one or more layersapplied on top of a substrate; and wherein chemically reactivefunctional groups incorporated in the coating react with one or morechemical stripping agents effecting the removal of the coating from thesubstrate.

[0007] A coating composition is provided comprising an emulsion polymerthat is both radiation curable, removable and includes chemicallyreactive functional groups in the coating that react with one or morechemical stripping agents, effecting the removal of the coating from asubstrate. In one embodiment, the coating is applied directly to thesubstrate. In a separate embodiment, the coating includes an emulsionpolymer that is both radiation curable, removable and incorporatedwithin one or more layers applied on top of a substrate. In a separateembodiment, the coating includes an emulsion polymer that is bothradiation curable, removable and is applied on top of a base coat.

[0008] Accordingly, there is provided a floor finishing systemcomprising a removable curable coating and a base coat composition,wherein the base coat further comprises a conventional coatingcomposition that is in contact with a substrate and is removable fromthe substrate using one or more chemical stripping agents and whereinthe removable curable coating is in contact with the base coatcomposition. In a separate embodiment there is provided a floorfinishing system comprising a removable curable coating that is incontact with a substrate and is removable from the substrate using oneor more chemical stripping agents.

[0009] There is also a provided a method for applying a highlycross-linked coating as one or more layers to a substrate andsubsequently removing all coating layers from a substrate comprising thesteps of:

[0010] (a) applying one or more layers of a coating comprising acurable, removable emulsion polymer;

[0011] (b) curing the composition to form a highly cross-linked coatingover the substrate by exposing the composition to ultraviolet radiation;and

[0012] (c) removing all coating layers from the substrate by exposingthe coating to one or more chemical stripping agents.

[0013] The present invention also provides a method for preparing a UVcurable, removable multi-layer coating composition comprising (a)applying a first-coating composition to a substrate wherein thefirst-coating composition comprises a polymer product having a gelfraction of 0.3 to 0.95 in a solvent selected from one or more ofacetone and tetrahydrofuran and wherein the first-coating composition isapplied in one or more separate applications, allowing the first-coatingcomposition to dry after each application; and (b) applying one or morelayers of a coating comprising a curable, removable emulsion polymer.

[0014] The present invention further provides a coated surfacecomposition comprising a substrate bearing a multi-layer coatingcomprising (a) a first-coating composition disposed upon the substrate,wherein the first coating composition comprises a polymer product havinga gel fraction in acetone of 0.3 to 0.95; and (b) a second-coatingcomposition disposed upon the first coating composition, wherein thesecond coating composition comprises a curable, removable emulsionpolymer; wherein the substrate is selected from one or more of flooring,wall, ceiling and tile materials.

[0015] Conventional easily removable protective coatings in the form ofpolishes are typically intended as sacrificial coatings to protect anunderlying substrate by accepting and resisting marks, soils, scuffs,abrasion and scratches encountered in the normal use of the substrate,and, when the useful or aesthetic life of the protective coating hasexpired, the polish can be easily removed from the substrate to bereplaced with a new coating. Typically, removability has been providedfor these floor polishes by (i) incorporating metal ion cross-linkingagents into polymers containing an excess of free carboxyl groups suchthat the metal ion cross-linking agents react with residual carboxylgroups (for example, from polymerized acrylic or methacrylic acid) or by(ii) the use of high levels of acid containing Alkali Soluble Resins(ASR) as formulation adjuncts. The relative excess of free carboxylgroups allows these coating compositions to swell when exposed tochemical swelling agents (such as aqueous ammonia or amines), thusrendering the coating easily removable when exposed to the strippingprocess; the swelling phenomenon interferes with cohesion and adhesionof the coating to the substrate such that film integrity is disrupted,thus facilitating removal of the coating from the substrate, forexample, hard surfaces such as flooring, ceiling, walls and tiles.However, if sufficient acid functionality is added to the polish polymeror polish formulation for adequate long-term removability, resistance ordurability of the polish film to scrubbing with alkaline detergentsolutions is significantly diminished. Alternatively, if the acidfunctionality in the polish polymer or the amount of ASR in theformulation is reduced in order to allow for aggressive cleaningoperations, then long-term ease of removability is compromised.Inventors have discovered a new solution to providing highly durablecoatings that are easily removed after application to a substrate.Inventors have discovered that highly cross-linked, UV cured coatingsprepared from certain emulsion polymers have enhanced durability and areeasily removed under conventional stripping conditions.

[0016] As used herein, the following terms have the designateddefinitions, unless the context clearly indicates otherwise. The term“alkyl (meth)acrylate” refers to either the corresponding acrylate ormethacrylate ester; similarly, the term “(meth)acrylic” refers to eitheracrylic or methacrylic acid and the corresponding derivatives, such asesters or amides. The term “copolymer” refers to polymer compositionscontaining units of two or more different monomers. The term“radiation-curable” in reference to coating compositions, refers tocoating compositions that form a hardened coating upon exposure toradiation such as UV radiation, visible light or electron beam. Theterms “ultraviolet radiation” and “UV radiation” are usedinterchangeably to refer to the spectrum of light having wavelengths inthe range from about 180 to 400 nanometers; visible light refers to thespectrum of light having wavelengths in the range from about 400 to 800nanometers. The term “coating composition” refers to aqueous-based orsolvent-based liquid compositions that can be applied to a substrate andthereafter solidified (for example, by radiation, air curing, postcross-linking or ambient temperature drying) to form a hardened coatingon the substrate.

[0017] The term “substrate” refers to any surface (vertical, horizontalor inclined, such as flooring, walls, ceilings and stairways) upon whichthe coating compositions of the invention may be applied, and includes,for example, flooring, wall, ceiling and tile materials such as vinylfloor tiles (including tiles optionally coated with sealer or primer),ceramic tiles, wood, metal, concrete, marble, slate and simulatednatural stone. Preferably the flooring, wall, ceiling and tile materialsare selected from one or more of the group consisting of vinyl polymer,concrete, marble, ceramic and wood.

[0018] The term “gel fraction value” refers to a numerical indexrelating swellability of a polymer in an organic solvent and the ease ofremovability of the corresponding coating composition under conventionalstripping conditions; gel fraction values greater than 0.95 indicatenegligible swellability and polymers having values below 0.95 areconsidered swellable. The term “sealer” and “base coat” and “primer” areused interchangeably to refer to coating compositions that may beapplied directly to a substrate and dried prior to application ofcoating compositions used in the method of the present invention; basecoat or sealer compositions are considered to be removable underconventional stripping conditions for purposes of the present invention.

[0019] All percentages referred to will be expressed in weight percent(%), based on total weight of polymer or composition involved, unlessspecified otherwise. The following abbreviations are used herein:g=grams, cm=centimeters, cm²=square centimeters, mJ=millijoules. Unlessotherwise specified, ranges listed are to be read as inclusive andcombinable and temperatures are in degrees centigrade (° C).

[0020] For the purposes of the present invention, conventional strippingconditions refer to the use of some form of mechanical abrasion (forexample, wiping, brushing, mopping or scrubbing) in the presence ofsolutions (aqueous, aqueous-alcohol or solvent-containing mixtures)containing amine or ammonia (typical contact times of at least 10 to 30minutes), to provide removal of the entire coating from a coatedsubstrate.

[0021] In one embodiment of the invention, the removable radiationcurable coatings comprise multi-stage emulsion polymers including atleast one multifunctional monomer. The multistage emulsion polymers areeasily applied to substrates and provide durable, highly cross-linkedcoatings upon curing by exposure to low intensity radiation. Themultifunctional monomer incorporated into the multi-stage emulsionpolymers include chemically reactive functional groups that effect theeasy removal of the highly cross-linked coatings from substrates. Inaddition, the removable curable coatings are applied to substrateswithout objectionable odors, cured to form optically transparentcoatings over substrates and are easily removed from substrates usingconventional chemical stripping agents.

[0022] The polymers of this invention are multi-staged latex particlesmade up of at least two mutually incompatible copolymers as described inU.S. Pat. Nos. 5,306,744 and 5,409,971. The resulting polymer aremultifunctional. Multifunctional polymers refers to polymer having aplurality of ethylenically unsaturated groups and a plurality ofchemically reactive functional groups. “Latex” as used herein refers toa dispersion of a water-insoluble polymer which may be prepared byconventional polymerization techniques such as, for example, by emulsionpolymerization. These mutually incompatible copolymers may be present inthe following morphological configurations, for example, core/shell,core/shell particles with shell stages incompletely encapsulating thecore, core/shell particles with a multiplicity of cores, core/shellparticles with a multiplicity of shells, interpenetrating networkparticles, and the like. In all of these cases the majority of thesurface area of the particle will be occupied by at least one outerstage and the interior of the particle will be occupied by at least oneinner stage.

[0023] The mutual incompatibility of two copolymer compositions may bedetermined in various ways known in the art. For example, scanningelectron microscopy using staining techniques to emphasize thedifference between the appearance of the phases or stages is one suchtechnique.

[0024] The functionalized multi-stage latex polymer of this inventionshall be described as containing a “first stage” and a “second stage.”The “second stage” as used herein does not mean to exclude thepossibility that one or more polymers can be interposed between orformed on the first stage polymer and before the second stage polymer.In addition, “first stage” and “second stage” are not used to imply inwhat sequence the polymers are formed.

[0025] The first stage polymer may be formed from a mixture ofco-monomers containing less than about 10% by weight of at least onecross-linking co-monomer, preferably at a level of from about 1% byweight of the first stage co-monomers to about 5% by weight of the firststage co-monomers.

[0026] “Cross-linking co-monomer” as used herein refers to apolyethylenically unsaturated monomer or mixture of ethylenicallyunsaturated monomers which cross-links a polymer composition during theinitial formation thereof. Subsequent drying or other curing techniquesare not required. Co-monomers of this type are well known and includemonomers wherein the functionality is of substantially equivalentreactivity so that uniform cross-linking occurs. Typically, suchco-monomers contain at least two addition polymerizable vinylidenegroups and are α,β-ethylenically unsaturated monocarboxylic acid estersof polyhydric alcohols containing 2-6 ester groups. Suitablecross-linking co-monomers include alkylene glycol diacrylates anddimethacrylates, such as for example, ethylene glycol diacrylate,ethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate,1,4-butylene glycol diacrylate propylene glycol diacrylate andtriethylene glycol dimethylacrylate; 1,3-glycerol dimethacrylate;1,1,1-trimethylol propane dimethacrylate; 1,1,1-trimethylol ethanediacrylate; pentaerythritol trimethacrylate; 1,2,6-hexane triacrylate;sorbitol pentamethacrylate; methylene bis-acrylamide, methylenebis-methacrylamide, divinyl benzene, vinyl methacrylate, vinylcrotonate, vinyl acrylate, vinyl acetylene, trivinyl benzene, triallylcyanurate, divinyl acetylene, divinyl ethane, divinyl sulfide, divinylether, divinyl sulfone, diallyl cyanamide, ethylene glycol divinylether, diallyl phthalate, divinyl dimethyl silane, glycerol trivinylether, divinyl adipate; dicyclopentenyl (meth)acrylates;dicyclopentenyloxy (meth)acrylates; unsaturated esters of glycolmonodicyclopentenyl ethers; allyl esters of α,β-unsaturated mono- anddicarboxylic acids having terminal ethylenic unsaturation includingallyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate,diallyl itaconate and the like. The term “(meth)acrylate” refers toacrylate or methacrylate. Allyl methacrylate is preferred. In oneembodiment, the multi-stage polymer includes a highly cross-linkedpolymer as a first stage or core.

[0027] The balance of the first stage polymer can be formed from a widevariety of monomers or mixture of monomers. These monomers includeacrylic acid ester monomers, including methyl acrylate, ethyl acrylate,propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate,secondary butyl acrylate, t-butyl acrylate, pentyl acrylate, neopentylacrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctylacrylate, 2-ethylhexyl acrylate, decyl acrylate, isodecyl acrylate,lauryl acrylate, bornyl acrylate, isobornyl acrylate, myristyl acrylate,pentadecyl acrylate, stearyl acrylate and the like; methacrylic acidester monomers, including methyl methacrylate, ethyl methacrylate,propyl methacrylate, isopropyl methacrylate, butyl methacrylate,isobutyl methacrylate, hexyl methacrylate, octyl methacrylate, isooctylmethacrylate, decyl methacrylate, isodecyl methacrylate, laurylmethacrylate, bornyl methacrylate, isobornyl methacrylate, myristylmethacrylate, pentadecyl methacrylate, stearyl methacrylate and thelike; acrylic acid, methacrylic acid, itaconic acid, maleic acid,fumaric acid, styrene, substituted styrenes, butadiene, acrylonitrile,ethylene, vinyl acetate, and the like may be used.

[0028] Hydrophobic monomers, such as for example, butyl acrylate andstyrene, are preferred monomers for the balance of the first stagepolymer to impart water resistance and durability to the removableradiation curable coating.

[0029] The second stage polymer of this invention containsα,β-unsaturated carbonyl functional groups which permit the multistagepolymer to undergo curing by irradiation. Suitable monoethylenicallyunsaturated functional groups include (meth)acrylate, fumarate, maleate,cinnamate and crotonates. (Meth)acrylate functional groups arepreferred. Alkali soluble emulsion (ASE) polymers and hydrophobicallymodified alkali soluble emulsion (HASE) polymers are for the balance ofthe second stage or shell of the polymer to effect the easy removal ofthe highly cross-linked coating using conventional chemical strippingagents.

[0030] The removable radiation curable coating preferably comprises amulti-stage emulsion polymer that includes a highly cross-linked core orfirst stage and alkali soluble polymer shell or second stage havingresidual ethylenically unsaturated groups. In a separate embodiment, theremovable radiation curable coating comprises a multi-stage emulsionpolymer that includes a highly cross-linked core or first stage andalkali soluble polymer shell that is then reacted with a multifunctionalmonomer to provide a post functionalized shell having residualethylenically unsaturated groups.

[0031] As used herein, acrylate and methacrylate are referred to as“(meth)acrylate”, acryloyl group and methacryloyl are referred to as“(meth)acryloyl” and acrylic acid and methacrylic acid are referred toas “(meth)acrylic acid”. “Monomer” refers to any chemical species havingat least one free radical polymerizable group (ethylenically unsaturatedcompounds, e.g. acrylate, methacrylate).

[0032] The functionalized multi-stage latex polymer emulsion may have alevel of solids from about 25% to about 50%, preferably from about 35%to about 45%.

[0033] The α,β-unsaturated carbonyl functional groups may beincorporated into the second stage polymer by employing a multistagepolymer wherein the second stage polymer is formed from about 30% byweight to about 60% by weight, preferably from about 35% by weight toabout 45% by weight, of an acid-containing co-monomer or mixturesthereof. Useful acid-containing co-monomers include those co-monomershaving carboxylic acid functionality, such as for example acrylic acid,methacrylic acid, itaconic acid, fumaric acid, citraconic acid;phosphoethyl methacrylate and the like.

[0034] The acid functionality is at least partially neutralized using asuitable base, such as for example, ammonium hydroxide, sodiumhydroxide, potassium hydroxide, sodium carbonate and the like. Inaddition, a quaternary ammonium phase transfer agent, such as forexample tetra-butyl ammonium hydroxide, diallyl dimethyl ammoniumhydroxide and the like, may be added. The base is added at a level offrom about 10 mole % on acid to about 15 mole % on acid if quaternaryammonium phase transfer agent is present. The base is added at a levelof about 30 mole % on acid if no quaternary ammonium phase transferagent is present.

[0035] The multi-stage polymer having partially neutralizedacid-functionality in the second stage is then reacted with amultifunctional monomer. Multifunctional monomer refers to a monomerhaving at least one ethylenically unsaturated group and at least onechemically reactive functional group. Suitable multifunctional monomersinclude but are not limited to monoethylenically unsaturatedmonoepoxides, monoethylenically unsaturated amines, monoethylenicallyunsaturated diamines and monoethylenically unsaturated alcohols andpolyols.

[0036] Suitable monoethylenically unsaturated monoepoxides includeglycidyl (meth)acrylate, allyl glycidyl ether, glycidyl cinnamates,glycidyl crotonates, glycidyl itaconates, glycidyl norbornenyl ester,glycidyl norbornenyl ether and the like. In a preferred embodiment, themulti-stage polymer having partially neutralized acid-functionality inthe second stage is then reacted with a monoethylenically unsaturatedmonoepoxide.

[0037] The weight ratio of polymer stages including the multifunctionalmonomer to remaining polymer stages is from 20:80 to 70:30. In oneembodiment, the functionalized multistage latex polymer of thisinvention has a weight ratio of first stage polymer to second stagepolymer of from about 20:80 to about 70:30 and preferably from about30:70 to about 50:50.

[0038] In one embodiment the acrylic-based polymer product, comprises,as polymerized monomer units: (a) zero to 60 percent, based on weight ofthe polymer, of a mono-ethylenically unsaturated monomer containing acarboxylic acid functional group; (b) 1 to 80 and preferably 5 to 70percent, based on weight of the polymer, of a (meth)acrylic monomercontaining functional groups selected from one or more monoethylenicallyunsaturated monoepoxides, glycidyl (meth)acrylate, allyl glycidyl ether,glycidyl cinnamates, glycidyl crotonates, glycidyl itaconates, glycidylnorbornenyl ester, glycidyl norbornenyl ether and other acrylatecontaining pendant vinyl groups; (c) zero up to 70, preferably 10 to 40percent, based on weight of the polymer, of one or more vinyl aromaticmonomers; (d) zero up to 90, preferably 20 to 80 percent, based onweight of the polymer, of one or more (C₁-C₂₀)alkyl (meth)acrylate estermonomers; and (e) zero up to 10 percent, based on weight of the polymer,of one or more other co-polymerizable monomers. Preferably, the polymerproduct is a radiation-curable composition where the polymer productcomprises, as polymerized monomer units methacrylic acid, glycidylmethacrylate and one or more (C₁-C₂₀)alkyl (meth)acrylate estermonomers, preferably selected from one or more of butyl acrylate andmethyl methacrylate. U.S. Pat. Nos. 5,306,744 and 6,197,844 may beconsulted for further general and specific details on the preparation ofthe polymers. Optionally, the polymer also includes zero up to 90,preferably 5 to 80 and more preferably 20 to 75 percent, based onequivalents of carboxylic acid groups of the first polymer, ofpolyvalent metal ion, preferably selected from one or more of the groupconsisting of zinc, calcium, magnesium and zirconium. U.S. Pat. Nos.4,150,005, 4,517,330, 5,149,745 and 5,676,741 may be consulted forfurther general and specific details of metal cross-linking agents.

[0039] In a separate embodiment the shell or outer stage of themulti-stage emulsion polymer comprises an alkali soluble emulsionpolymer or a hydrophobically modified emulsion polymer. Alkalisoluble/swellable emulsion (ASE) polymers are polyelectrolytes based onacid-containing emulsion polymers disclosed in U.S. Pat. Nos. 3,035,004and 4,384,096 (HASE polymers) and Great Britain Pat. No. 870,994. Theinventors have discovered that adjusting the type and level of acidmonomers and co-monomers in ASE polymers coupled with the degree ofneutralization to achieve optimum charge density to afford polymers thatare stable, having a low degree of swelling and insoluble in an aqueoussystem of relatively high ionic strength. The polymers usefully employedin the invention have varying degree of neutralization of the carboxylicacid groups ranging from partially to completely neutralized. Thepolymers can be characterized as incorporating an ionic strength triggeror referred to as ionic strength sensitive polymers. Changes in theionic strength of the aqueous system to lower levels results in the apolymer that rapidly disperses, dissolves or swells to a significantextent in the aqueous system.

[0040] Suitable monoethylenically unsaturated monoamines include but arenot limited to (meth)acrylamide, aminoalkyl(meth)acrylates such asaminoethylacrylate, aminodialkylacrylates such asN,N-dimethyl-aminoethyl(meth)acrylate,N,N-dimethyl-aminopropyl(meth)acrylate, andN,N-dimethyl-aminopropyl(meth)acrylamide. Suitable monoethylenicallyunsaturated diamines include for example ethylene diaminealkyl(meth)acrylates. Suitable monoethelenically unsaturated alcoholsinclude for example 2-hydroxyethyl(meth)acrylate and (meth)acrylicesters of polyethylene glycols.

[0041] It is preferred that the coating formulation contains less thanabout 5.0% by weight, more preferably less than about 3.0% by weight,most preferably less than about 0.5% by weight of water solublematerials including inorganic salts and the residual monomer byproductsof the hydrolysis of the monoethylenically unsaturated monoepoxide, suchas dihydroxypropyl methacrylate from the hydrolysis of glycidylmethacrylate and glycerol and methacrylic acid from the furtherhydrolysis of hydroxypropyl methacrylate. Dried coating formulationshaving less than 5.0% by weight of these byproducts have improvedresistance to water. Suitable methods for removing water solublematerials include treatment by ion exchange resins, filtration and thelike.

[0042] Other suitable highly durable non-removable compositions normallyuseful as top coats can be rendered removable according to theinvention, including those based on polymers having a gel fraction valueof greater than 0.95 and up to 0.99. The top coating compositions may beaqueous-based or solvent-based. While not wishing to be bound by theory,it is believed that the highly durable top-coating compositions shouldpossess some permeability, hence a gel fraction value less than 1.0, tothe components (solvent or amine) used in conventional strippingoperations so that some portion of the stripping solution may haveaccess to the base-coating composition (over which the top-coatingcomposition is disposed) in order to swell and subsequently remove theentire multi-layer coating composition.

[0043] Other suitable compositions for use as the highly durabletop-coat compositions in the method of the present invention include,for example, polymers described below:

[0044] (I) Acrylic-based polymer product derived from combining (1) afirst-stage polymer comprising, as polymerized monomer units (a) 0.1 to30 percent, based on weight of the first-stage polymer, of amonoethylenically unsaturated monomer containing a carboxylic acidfunctional group; (b) zero up to 60 percent, based on weight of thefirst-stage polymer, of a (meth)acrylic monomer containing one or morependant reactive functional groups selected from vinyl, epoxy, hydroxy,thiol, acetoacetoxy and amino groups; (c) zero up to 70 percent, basedon weight of the first-stage polymer, of one or more vinyl aromaticmonomers; (d) zero up to 90 percent, based on weight of the first-stagepolymer, of one or more (C₁-C₂₀)alkyl (meth)acrylate ester monomers; and(e) zero up to 10 percent, based on weight of the first-stage polymer,of one or more other co-polymerizable monomers; with (2) apolyfunctional cross-linker agent comprising pendant functional groupsselected from one or more of isocyanate, carbodiumide, aziridinyl,vinyl, hydroxy, thiol, acetoacetoxy, amino and epoxy groups; wherein,the first-stage polymer has a number average molecular weight fromgreater than 5,000 up to 2,000,000; and the polyfunctional cross-linkeragent is used in an amount sufficient to provide from 0.2 to 10equivalents of pendant functional group per equivalent of correspondingpendant reactive functional group in the first-stage polymer.

[0045] One embodiment of the polymer (I) is represented by the polymerproduct derived from combining (1) a first-stage polymer comprising, aspolymerized monomer units: (a) 1 to 20 percent, based on weight of thefirst-stage polymer, of monoethylenically unsaturated monomer containinga carboxylic acid functional group; (b) 2 to 60 percent, based on weightof the first-stage polymer, of a (meth)acrylic monomer containing one ormore pendant reactive hydroxy functional groups; and (c) zero up to 20percent, based on weight of the first-stage polymer, of one or more(C₁-C₂₀)alkyl (meth)acrylate ester monomers; with (2) a polyfunctionalcross-linker agent comprising pendant isocyanate functional groups.

[0046] (II) A polyurethane polymer that is the reaction product of atleast one polyol with a polyisocyanate reactant comprising aspolymerized units: (a) zero up to 20 percent, based on weight of thepolyurethane polymer, of a polyol containing a carboxylic acidfunctional group; (b) 10 to 80 percent, based on weight of thepolyurethane polymer, of polyol selected from one or more of saturatedand unsaturated polyhydric alcohols, polyester polyols, polyetherpolyols and polycarbonate polyols; (c) 10 to 30 percent, based on weightof the polyurethane polymer, of a polyisocyanate reactant selected fromone or more of aromatic, cycloaliphatic and aliphatic polyisocyanates;and (d) zero up to 40 percent, based on weight of the polyurethanepolymer, of a polyether selected from one or more of cappedpolyalkyleneglycols and polyether polyols.

[0047] Preferably the polyurethane polymer is provided in the form of adispersion in water. Suitable polyol reactants include, for example,polyols selected from one or more of saturated and unsaturatedpolyhydric alcohols (such as ethylene glycol, propylene glycol,1,4-butanediol, 1,4-butenediol and cyclohexanedi-methanol), polyesterpolyols from the reaction of saturated and unsaturated polyhydricalcohols with saturated and unsaturated polycarboxylic acids (such asmaleic acid, itaconic acid, succinic acid, terephthalic acid, phthalicanhydride and dimethyl terephthalate), polyether polyols (such aspolyalkylene-glycols) and polycarbonate polyols (such as those formedfrom the reaction of polyhydric alcohols with diaryl carbonates).Optionally, polyols containing a carboxylic acid functional group mayalso be used, such as polyhydroxycarboxylic acids, for example,2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid and2,2-ddimethylolvaleric acid. Optionally, capped polyalkyleneglycols(monohydric hydroxy compounds) may be used in addition to the polyols,for example, poly(ethyleneglycol) methyl ether may be used to introducepolyether content into the polyurethane. Typically some portion of thepolyol reactant is derived from polyols containing ionic or hydrophilicgroups.

[0048] Suitable polyisocyanate reactants include, for example, aromatic,cycloaliphatic and aliphatic polyisocyanates such as1,6-diisocyanatohexane (HDI), 4,4′-diisocyanatodicyclohexylmethane,1,4-diusocyanatobutane, 2,4- and 2,6-tolylene diisocyanate,4,4′-diisocyanatodiphenylether, methylene-bis(4-phenylisocyanate),m-phenylene diisocyanate and 1,2,4-benzene triisocyanate.

[0049] For example, a typical polyurethane polymer may contain 10 to80%, preferably 30 to 70%, of polyol component; 5 to 40%, preferably 10to 30%, of polyisocyanate component; and optionally zero to 40%,preferably 10 to 30%, of polyether component.

[0050] Typically the polyurethane polymer is formed by adding a polyoltogether with a catalyst (for example, 0.01 to 0.06% of di-butyl tindilaurate or tin octoate) to a reaction vessel in the presence ofsolvent (such as N-methyl pyrrolidone, N,N-dimethyl formamide, methylethyl ketone, toluene and mixtures thereof) and heating the mixture at70-100° C. with continuous or intermittent addition, over about 0.5-4hours, of a polyisocyanate reactant. After complete addition of thepolyisocyanate reactant the reaction mixture is maintained at 80-100° C.(typically 2-4 hours) to reduce the residual isocyanate content to belowabout 8%, based on weight of polymer. The reaction mixture is thencooled and any ionic groups present in the reaction product areneutralized by the addition of a weak base (for example, triethylamine,trimethylamine, dimethylethanolamine, triethanolamine ordimethylaminopropanol). The reaction mixture is then dispersed intowater to form the polyurethane dispersion, typically having a finalpolymer solids level of about 20 to 60%, based on total weight of thedispersion. Optionally, a difunctional amine compound (for example,ethylenediamine, hexamethylene diamine or mixtures thereof or apolyaziridinyl cross-linker agent may be included in the water medium toprovide chain extension of the polyurethane. Alternatively, additionalcross-linking may be introduced via air oxidation cure involving othercoating formulation components. U.S. Pat. No. 6,384,131 may be consultedfor further general and specific details on the preparation ofpolyurethane dispersions useful as a top-coating compositions.

[0051] (III) Acrylic-based polymer product derived from combining (1) afirst-stage polymer comprising, as polymerized monomer units: (a) zeroup to 20, preferably 1 to 5 percent, based on weight of the first-stagepolymer, of monoethylenically unsaturated monomer containing acarboxylic acid functional group; (b) 0.5 to 100, preferably 1 to 40 andmore preferably 5 to 20 percent, based on weight of the first-stagepolymer, of a (meth)acrylic monomer containing one or more pendantreactive acetoacetoxy functional groups; (c) zero up to 95, preferably40 to 90 percent, based on weight of the first-stage polymer, of one ormore (C₁-C₂₀)alkyl (meth)acrylate ester monomers; (d) zero up to 10percent, based on weight of the first polymer, of one or more otherco-polymerizable monomers; with (2) an amine-containing reactantselected from one or more of the group consisting of polyamine andaminosilane reactants, in an amount sufficient to provide from 0.1 to1.5, preferably from 0.3 to 1.0, equivalents of amino functional groupper equivalent of acetoacetoxy group in the first-stage polymer; andcross-linking the polymer product through formation of diamine orsiloxane linking groups.

[0052] Suitable polyamine reactants useful in the preparation oftop-coating compositions involving polymer (III) include, for example,polyamines containing 2 to 100 carbon atoms where at least two of theamino groups are primary amine groups.

[0053] Suitable aminosilane reactants useful in the preparation oftop-coating compositions involving polymer (7) include, for example,trimethoxysilylpropyl-diethylenetriamine,N-methylaminopropyltrimethoxy-silane,aminoethylamino-propylmethyldimethoxysilane,aminoethylamino-propyltrimethoxysilane,amino-propylmethyldimethoxysilane, aminopropyltrimethoxysilane,polymeric amino-alkylsilicone,aminoethylaminoethylaminopropyltrimethoxysilane,N-methylamino-propyltrimethoxysilane, methylaminopropyltrimethoxysilane,aminopropyl-methyldiethoxysilane, aminopropyltriethoxysilane,4-aminobutyltriethoxy-silane and oligomeric aminoalkylsilanes.Preferably the aminosilane reactant is selected from one or more ofaminopropyltrimethoxysilane, aminoethylamino-propyltrimethoxysilane,aminopropylmethyldiethoxysilane andaminoethyl-aminopropylmethyldimethoxysilane. Preferably, the polymerproduct is derived from combining (1) a first-stage polymer comprising,as polymerized monomer units: (a) 1 to 5 percent, based on weight of thefirst-stage polymer, of monoethylenically unsaturated monomer containinga carboxylic acid functional group; (b) 5 to 20 percent, based on weightof the first-stage polymer, of a (meth)acrylic monomer containing one ormore pendant reactive acetoacetoxy functional groups; and (c) 40 to 90percent, based on weight of the first-stage polymer, of one or more(C₁-C₂₀)alkyl (meth)acrylate ester monomers; with (2) an aminosilanereactant in an amount sufficient to provide from 0.3 to 1.0 equivalentsof amino functional group per equivalent of acetoacetoxy group in thefirst-stage polymer. U.S. Pat. No. 5,426,142 may be consulted forfurther general and specific details on the preparation ofaminosilane-modified polymers representative of polymer (III).

[0054] Representative suitable monomer components of polymers (I-III)are the same as corresponding monomer component types for polymersdescribed previously and for polymers used to form a base coat over thesubstrate (polymers IV-VI).

[0055] Methods for the preparation of the aqueous dispersible polymersof the coating compositions useful in coatings of the invention and themethod of the present invention are well known in the art. Both singleand multi-stage polymers may be solution, dispersion or emulsionpolymers; preferably the polymers are emulsion polymers. The practice ofemulsion polymerization is discussed in detail in D. C. Blackley,Emulsion Polymerization (Wiley, 1975). Suitable monomers may beemulsified with anionic or nonionic dispersing agents; for example, 0.5%to 10% based on the weight of total monomers being used. Acidic monomersare water soluble and thus serve as dispersing agents which aid inemulsifying the other monomers used. A polymerization initiator of thefree radical type, such as ammonium or potassium persulphate, may beused alone or in conjunction with an accelerator, such as potassiummetabisulfite or sodium thiosulfate. The initiator and accelerator,commonly referred to as catalysts, may be used in proportions of 0.1% to2%, each based on the weight of monomers to be co-polymerized. Thepolymerization temperature is typically from ambient temperature up to90° C. Examples of emulsifiers suitable for emulsion polymerizationinclude, for example, alkaline metal and ammonium salts of alkyl, aryl,alkaryl and aralkyl sulfonates, sulfates, polyether sulfates, andalkoxylated derivatives of fatty acids, esters, alcohols, amines, amidesand alkylphenols. Chain transfer agents, including mercaptans,polymercaptans and polyhalogen compounds, may be used in thepolymerization mixture to control molecular weight of the polymer.

[0056] Among the suitable second-coating compositions areradiation-curable compositions, multi-component compositions containinga cross-linking agent, and highly pre-cross-linked compositions thatform coating films. Representative of radiation-curable coatings arecompositions comprising polymerized units of a polyfunctionalisocyanurate having at least three terminal reactive groups reacted witha hydroxyalkyl (meth)acrylate; U.S. Pat. No. 6,197,844 may be consultedfor further general and specific details on the use of this type ofcoating composition.

[0057] Photo-polymerization of the curable composition involvesirradiation of ethylenically unsaturated compounds in the presence of aphoto-initiator, where “photo-initiator” refers to any material orcombination of materials that interact with light to generate freeradicals suitable for initiating free radical polymerization.Photo-polymerizations occur when radicals are produced by ultraviolet(UV) or visible light irradiation, or combination thereof, of a freeradical polymerizable reaction system. Photo-polymerization may beapplied in the formation of protective coatings for metal, paper, woodand plastic substrates. Typical applications involve a combination ofphoto-polymerization and cross-linking, with the cross-linking achievedby the use of polyunsaturated monomers. Suitable systems includeacrylate, unsaturated polyester and styrenic-based compositions.

[0058] Additionally, UV curable protective coatings may be applied tovinyl flooring during sheet manufacturing processes to provide gloss andabrasion resistance. The curing of these coating compositions isconducted using high intensity light in an inert atmosphere to minimizethe deleterious effects of oxygen on the curing process. Afterapplication to a substrate, these protective coatings typically cannotbe easily stripped from the flooring to which they were applied usingconventional stripping methods, such as application of a chemicalstripping composition with a stripping pad or brush.

[0059] A formulated coating may optionally contain an ultravioletphoto-initiator. The low amount of photo-initiator which can optionallybe employed is an additional advantage of the present invention. Thephoto-initiator may be added to the composition from about 0.2% byweight of total non-volatiles to about 1.0% by weight of totalnon-volatiles. Useful photo-initiators include cleavage-type initiators,halogenated polynuclear ketones, such as chlorosulfonated benzanthones,chlorosulfonated fluorenones, α-haloalkylated benzanthrones, andα-haloalkylated fluorenone as disclosed in U.S. Pat. Nos. 3,827,957 and3,827,959; benzoin, its ethers, such as methyl ether, ethyl ether,isopropyl ether, butyl ether, octyl ether and the like; carbonylcompounds such as diacetyl, benzil and the like; sulfur compounds suchdiphenyl sulfide, dithiocarbamate and the like; α-chloromethylnaphthalene and anthracene. Other useful photo-initiators includealkylphenones and benzophenones as disclosed in U.S. Pat. No. 3,759,807.Photo-initiators suitable for pigmented coatings are suggested in U.S.Pat. Nos. 3,915,824 and 3,847,771.

[0060] The formulated coating may contain a thermal initiator if thecoating will be cured by heat or a catalyst if the coating will be curedby auto-oxidation. The thermal initiator is added to the compositionfrom about 0.5% by weight of total non-volatiles to about 2% by weightof total non-volatiles. Useful thermal initiators include azo compounds,such as azobisisobutyronitrile and the like; organic peroxides, such asketone peroxides, hydroperoxides, alkyl peroxides, acyl peroxides,peroxy esters and the like; and inorganic peroxides, such as ammoniumpersulfate, potassium persulfate, hydrogen peroxide and the like. Usefulcatalysts for auto-oxidative cure include the salts of cobalt, such ascobalt acetate, cobalt naphthenate and the like.

[0061] In addition, conventional coating components such as, forexample, pigments, dispersants, surfactants, coalescents (volatileorganic solvents including for example glycol ethers), plasticizers(non-volatile organic compounds including for example dibutylphthalate), wetting agents, rheology modifiers, thickeners, dryingretardants, antifoaming agents, colorants, waxes, preservatives, heatstabilizers, ultraviolet light stabilizers and the like may be used inthis invention.

[0062] Techniques for applying the radiation-curable coating includeroller coating, knife coating, squeegeeing, curtain coating, spraying,mopping and the like.

[0063] The formulated coating may be cured or cross-linked either byapplying radiation or by heating after most or all of the water hasevaporated from the mixture. Useful radiation includes ionizingradiation, electron beam radiation and ultraviolet radiation. Sources ofultraviolet radiation include sunlight, mercury lamp, carbon-arc lamp,xenon lamp and the like. Medium pressure mercury vapor lamps arepreferred.

[0064] “Ultraviolet radiation” and “UV radiation” are usedinterchangeably to refer to the spectrum of light comprising wavelengthswithin the range from about 180 nm to 400 nm. “Coatable composition”.means a liquid composition that can be applied to a substrate andthereafter solidified (e.g., by UV curing) to form a hardened coating onthe substrate. “Radiation curable”, in referring to the coatablecompositions, means that the coatable composition will form a hardenedcoating upon exposure to radiation such as UV radiation or visible light(e.g., 180 to 800 nm). “Substrate” refers to any surface upon which thecoatable compositions of the invention are applied and includes withoutlimitation, vinyl floor tiles (including tiles previously coated withfloor sealer or the like), concrete, ceramic tiles, wood, marble, andthe like.

[0065] In applying the coatings of the invention to a suitablesubstrate, it is preferred that the composition be applied in mannerwhich creates a coating no greater than about 1.3 millimeters inthickness in order to facilitate curing of the composition within theaforementioned time limits. Coatings of this thickness can be achievedby any of a number of known application techniques such as roll coating,squeegeeing, knife coating, curtain coating, spray coating, mopping andthe like. In applying the forgoing compositions to a substrate, suitablesubstrates include conventional floor tiles which may or may not bepreviously coated or sealed. When the substrate to be coated is vinyltile or the like, it is preferred that the substrate is first treatedwith a primer or sealer prior to the application of the UV curableinventive compositions to that substrate. A primer treatment of thesubstrate facilitates the ease at which the UV cured coating maysubsequently be removed from the tile or other substrate by a chemicalstripping formulation, for example. In order to promote adhesion of thecoatable composition to the substrate, an acrylated latex primer is mostpreferred. The acrylated latex compositions useful herein must have atleast one free-radically polymerizable group pendant from each latexparticle, and preferably more than one. The latex is hydrophobic innature, but may contain some hydrophilic groups.

[0066] In a separate embodiment of the invention the UV curable coatingsare deposited on a base coat which covers a substrate. When applying thebase coat to the substrate, it is desirable to provide a continuous filmover the surface of the substrate, adjusting the solids content of theprimer as needed to achieve such a film while using the least amount ofbase coat required to achieve a barrier layer with the desired adhesionproperties. Typically, the solids content of the base coat required fora wipe on coating (e.g., by hand) will be between about 2 and about 40%by weight, preferably between about 2 and about 30%, and more preferablybetween about 4 and about 25%. A wetting agent or defoamer may be addedto the latex emulsion to improve coating properties. The level of suchadditives will depend on the nature of the substrate and theconcentration of the latex emulsion.

[0067] One preferred latex emulsion for use as a base coat herein is theacrylated emulsion commercially available under the trade designation“ROSHIELD 3120” from Rohm and Haas Company, Philadelphia, Pa. Thisemulsion is available at a solids content of about 40.5% by weight, anda suitable base coat can be prepared by dilution of the concentratedemulsion at dilution weights ratio of up to about 20:1 (water:emulsion).An alternative base coat is an aqueous formulation comprising a blend orthe foregoing ROSHIELD 3120 acrylated latex with a second polymer,preferably the ammonium salt of a styrene maleic anhydride (SMA)copolymer (commercially available at a solids content of 38.5% under thetrade designation “SMA 1000A” from Atochem, Inc. of Malvern, Pa.). TheSMA is added to the base coat to act as a leveling aid. The weight ratioof the acrylate to the SMA copolymer in the primer is preferably betweenabout 3:1 and about 15:1. A small amount of surfactant may also beincluded in the base coat. A preferred base coat is one having a solidscontent of about 10% by weight, comprises about 24.4 wt % of theROSHIELD 3120 acrylated latex, about 73.2 wt % water, about 2.4 wt % SMA1000A copolymer and about 0.02 wt % surfactant or wetting agent such asthat commercially available under the trade designation “MASURF FS-230”from Mason Chemical Company, Arlington Heights, Ill.

[0068] The base coat may be applied to the substrate by any suitablemethod such as wiping, brushing, spraying, mopping and the like. Thelatex is allowed to dry, typically under ambient conditions, and the UVcurable compositions of the invention may then be applied thereover andcured, as described herein. Substrates such as PVC tiles, for example,coated with a UV curable multi-stage polymer of the invention arereadily stripped using a conventional chemical stripper. Substratescoated with the above acrylated latex base coat and then coated with aUV curable acrylate (e.g., a coatable composition) may be readilystripped using a conventional chemical stripper such as that describedbelow in the Examples. The stripped tiles present a very good appearancewith stripping appearing to occur at the surface of the tile.Corresponding tiles containing no base coat or coated with polymersI-III are slower to strip and generally do not strip cleanly (e.g., atthe substrate surface).

[0069] In the above described embodiment, the base coat can comprise acomponent of a floor finishing system that includes both the base coatas well as the coatable composition described herein. Although basecoats comprising the foregoing ROSHIELD 3120 acrylated latex (with orwithout added SMA copolymer) are preferred, other commercially availablematerials may also be used as base coats or floor polishes on certainsubstrates such as on PVC composition floor tile. Some suitable basecoats include various commercial floor sealers and floor polishes suchas those available under the trade designations “CORNERSTONE” (MinnesotaMining and Manufacturing Company, St. Paul, Minn.), “TOPLINE” (also fromMinnesota Mining and Manufacturing Company), “TECHNIQUE” (S.C. Johnsonof Milwaukee, Wis.), “CASTLEGUARD” (from Buckeye International, Inc. ofMaryland Heights, Mo.), “HIGH NOON” (from The Butcher Company ofMarlborough, Mass.) and “SIGNATURE” (from S. C. Johnson Profesional ofRacine, Wis.). It is also contemplated that the foregoing base coat,especially base coats comprising ROSHIELD 3120 acrylated latex, may beused in other applications outside the floor finishing art to apply anyof a variety of UV polymerizable polymers (e.g., other than theforegoing coatable compositions) to a substrate. Accordingly, the use ofa base coat provides a system and a method for coating a variety ofsubstrates with UV curable polymer and other durable, highlycross-linked polymers. In such a system and method, the resultingcoatings adhere well to the substrate and may also be more easilyremoved from the substrate by suitable stripper compositions. When usinga non-acrylated latex primer it is preferable to use a base coat whichhas a surface tension of at least 40 dynes/cm.

[0070] The cured coatings of the invention may be stripped from thesubstrates to which they are applied by the application of a suitablestripper. Conventional stripping conditions refer to the use of someform of mechanical abrasion (for example, wiping, brushing, mopping orscrubbing) in the presence of solutions (aqueous, aqueous-alcohol orsolvent-containing mixtures) containing amine or ammonia (typicalcontact times of at least 10 to 30 minutes), to provide removal of theentire coating from a coated substrate. Another suitable stripper is apH neutral formulation comprising a solvent, coupling agent (e.g.,hydrotrope) and water. Dye, fragrance and thickening agent may be addedto the stripper composition if desired. An effective stripperformulation for the floor finish compositions of the invention includesthose set forth below in the Test Methods.

[0071] The formulated coating containing the radiation-curablecomposition of this invention may be used as topcoats, intermediatecoats and base coats. The coatings are useful in applications whichrequire the reduced odor, toxicity and viscosity of aqueous-based,radiation-curable formulations, such as, for example, paints, includingwood lacquers; adhesives; inks, including screen printing inks andgravure and flexographic printing inks; plastics, including vinylsheeting, vinyl flooring and polyvinyl chloride flooring; fiber; paper,including overprint varnishes for paper and board; printed wiring boardsand electronic components; concrete; ceramic flooring including tiles;leather; masks, printing plates and other composites using UV cure. Thecoatings are particularly useful in applications on wood, such as, forexample, cabinets, furniture and flooring.

[0072] There is provided a floor finishing system comprising theremovable curable coating and a base coat composition, wherein the basecoat further comprises a conventional coating composition that is incontact with a substrate and is removable from the substrate using oneor more chemical stripping agents and wherein the removable curablecoating is in contact with the base coat composition.

[0073] By utilizing the removable radiation-curable composition of thisinvention, the need for a separate monomer component in a formulatedcoating is eliminated. The reduced or eliminated monomer levels improvethe safety, health and environmental implications of the uncured andcured coating formulation and eliminate the problems associated withformulating a coating having a separate monomer component, such as forexample mixing and dispersion problems. The functionality isincorporated directly into the multi-stage latex polymer providing a onecomponent system with reduced or eliminated levels of monomers.

[0074] Other suitable compositions for use as the easily removable basecoating composition are those having a gel fraction value in organicsolvent of 0.30 to 0.95, preferably from 0.4 to 0.9 and more preferablyfrom 0.5 to 0.8; the first-coating compositions may be aqueous-based orsolvent-based. Base coat floor polish compositions of the presentinvention typically comprise an aqueous suspension or dispersion of oneor more water insoluble emulsion polymers containing acid functionalresidues and, optionally, polyvalent metal ion or complex cross-linkingagents. Such base-coat compositions include, for example, acrylic-basedpolymer products selected from one or more of polymers (IV), (V) and(VI) described below:

[0075] (IV) First polymer comprising, as polymerized monomer units (a) 3to 90, preferably 6 to 30 and more preferably 10 to 15 percent, based onweight of the first polymer, of monoethylenically unsaturated monomercontaining a carboxylic acid functional group; (b) zero up to 40,preferably zero up to 25 and more preferably zero up to 15 percent,based on weight of the first polymer, of a (meth)acrylic monomercontaining one or more pendant reactive functional groups selected fromvinyl and hydroxy groups; (c) zero up to 80 percent, based on weight ofthe first polymer, of one or more vinyl aromatic monomers; (d) zero upto 97, preferably 20 to 90 and more preferably 60 to 80 percent, basedon weight of the first polymer, of one or more (C₁-C₂₀)alkyl(meth)acrylate ester monomers; (e) zero up to 10 percent, based onweight of the first polymer, of one or more other co-polymerizablemonomers; and (f) zero up to 90, preferably 5 to 80 and more preferably20 to 75 percent, based on equivalents of carboxylic acid groups of thefirst polymer, of polyvalent metal ion, preferably selected from one ormore of the group consisting of zinc, calcium, magnesium and zirconium.U.S. Pat. Nos. 4,150,005, 4,517,330, 5,149,745 and 5,676,741 may beconsulted for further general and specific details on the preparation offirst-coating compositions representative of polymer (IV).

[0076] (V) Second polymer comprising, as polymerized monomer units (a) 3to 30 and preferably 5 to 20 percent, based on weight of the secondpolymer, of a monoethylenically unsaturated monomer containingamino-group functionality; (b) 0.2 to 9, preferably 0.2 to 1.5 and morepreferably 0.4 to 1 percent, based on weight of the second polymer, of a(meth)acrylic monomer containing one or more pendant reactive functionalgroups selected from vinyl, epoxy and acetoacetoxy groups; (c) zero upto 80 percent, based on weight of the second polymer, of one or morevinyl aromatic monomers; (d) zero up to 97 percent, based on weight ofthe second polymer, of one or more (C₁-C₂₀)alkyl (meth)acrylate estermonomers; and (e) zero up to 10 percent, based on weight of the secondpolymer, of one or more other co-polymerizable monomers. U.S. Pat. No.5,676,741 may be consulted for further general and specific details onthe preparation of first-coating compositions representative of polymer(V).

[0077] (VI) Third polymer derived from combining (i) a first-stagepolymer comprising, as polymerized monomer units: (a) 5 to 50 percent,based on weight of the first-stage polymer, of a monoethylenicallyunsaturated monomer containing an acid functional group selected fromone or more of carboxylic, sulfonic and phosphonic groups; (b) zero upto 60 percent, based on weight of the first-stage polymer, of a(meth)acrylic monomer containing one or more pendant reactive functionalgroups selected from hydroxy, thiol, and amino groups; (c) zero up to 70percent, based on weight of the first-stage polymer, of one or morevinyl aromatic monomers; (d) 15 to 90 percent, based on weight of thefirst-stage polymer, of one or more (C₁-C₂₀)alkyl (meth)acrylate estermonomers; and (e) zero up to 10 percent, based on weight of thefirst-stage polymer, of one or more other co-polymerizable monomers;with (ii) a polyfunctional cross-linker agent comprising pendantfunctional groups selected from one or more of isocyanate, carbodiimide,aziridinyl and epoxy groups; wherein, the first-stage polymer has anumber average molecular weight from greater than 5,000 up to 2,000,000;and the polyfunctional cross-linker agent is used in an amountsufficient to provide from 0.2 to 5 equivalents of pendant functionalgroup per equivalent of corresponding pendant reactive functional groupin the first-stage polymer. The carboxylic acid functional groups of thefirst-stage polymer are included in the “corresponding pendant reactivefunctional groups” referred to above.

[0078] With reference to aforementioned polymers (IV), (V) and (VI),suitable carboxylic acid monomers include monoethylenically unsaturated(C₃-C₉)carboxylic acid monomers, such as unsaturated monocarboxylic anddicarboxylic acid monomers. For example, unsaturated monocarboxylicacids include acrylic acid (AA), methacrylic acid (MAA), α-ethacrylicacid, β,β-dimethylacrylic acid, vinylacetic acid, allylacetic acid,ethylidineacetic acid, propylidineacetic acid, crotonic acid,acryloxypropionic acid and corresponding alkali and metal salts thereof.Suitable unsaturated dicarboxylic acid monomers include, for example,maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconicacid, mesaconic acid, methylenemalonic acid and corresponding alkali andmetal salts thereof. Other suitable acidic monoethylenically unsaturatedmonomers include the partial esters of unsaturated aliphaticdicarboxylic acids (alkyl half esters); for example, the alkyl halfesters of itaconic acid, fumaric acid and maleic acid wherein the alkylgroup contains 1 to 6 carbon atoms (methyl acid itaconate, butyl aciditaconate, ethyl acid fumarate, butyl acid fumarate and methyl acidmaleate). Preferably, the monoethylenically unsaturated(C₃-C₉)carboxylic acid monomers are selected from one or more of acrylicacid, methacrylic acid and corresponding alkali and metal salts thereof.

[0079] With reference to aforementioned polymers (IV), (V) and (VI),suitable (meth)acrylic monomer containing pendant reactive functionalgroups include the following: hydroxy-functional (meth)acrylic monomers,for example, hydroxy(C₁-C₄)alkyl (meth)acrylates, such as hydroxyethylmethacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate andhydroxypropyl acrylate - preferably the hydroxy-functional (meth)acrylicmonomer is hydroxyethyl methacrylate (HEMA); amino-functional or aminogroup—containing (meth)acrylic monomers, for example,dimethylaminopropyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate,dimethylaminopropyl (meth)acrylate, t-butylaminoethyl (meth)acrylate andmethyaminoethyl acrylate; thiol-functional (meth)acrylic monomers, forexample, 2-mercaptopropyl methacrylate; vinyl-containing monomers, forexample allyl methacrylate and glycidyl (meth)acrylate; epoxy(meth)acrylic monomers, for example, glycidyl (meth)acrylate; andamine-reactive or air-curable (meth)acrylic monomers, for example, thosecontaining acetoacetoxy groups, such as acetoacetoxyethyl methacrylate(2-(methacryloyloxy)ethyl acetoacetate), acetoacetoxyethyl acrylate,acetoacetoxypropyl acrylate, acetoacetoxypropyl methacrylate,acetoacetoxybutyl acrylate, acetoacetoxybutyl methacrylate,2,3-di(aceto-acetoxy)propyl acrylate and 2,3-di(acetoacetoxy)propylmethacrylate. In addition to the above, non-(meth)acrylic monomerscontaining pendant reactive functional groups may be used, such asdivinylbenzene and allyl acetoacetate.

[0080] With reference to aforementioned polymers (1), (2) and (3),suitable vinylaromatic monomers include, for example, styrene, α-methylstyrene and substituted styrenes, such as vinyl toluene, 2-bromostyrene,4-chlorostyrene, 2-methoxystyrene, 4-methoxystyrene, α-cyanostyrene,allyl phenyl ether and allyl tolyl ether. When present, thevinylaromatic monomer is preferably styrene.

[0081] With reference to aforementioned polymers (1), (2) and (3),suitable (C₁-C₂₀)alkyl (meth)acrylate ester monomers include, forexample, methyl acrylate, ethyl acrylate, propyl acrylate, isopropylacrylate, butyl acrylate, isobutyl acrylate, secondary butyl acrylate,tertiary-butyl acrylate, methyl methacrylate, ethyl methacrylate, propylmethacrylate, isopropyl methacrylate, cyclopropyl, methacrylate, butylmethacrylate and isobutyl methacrylate, hexyl and cyclohexylmethacrylate, cyclohexyl acrylate, isobornyl methacrylate, 2-ethylhexylacrylate (EHA), 2-ethylhexyl methacrylate, octyl (meth)acrylate, decyl(meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl(meth)acrylate (also known as lauryl (meth)acrylate), tridecyl(meth)acrylate, tetradecyl (meth)acrylate (also known as myristyl(meth)acrylate), pentadecyl (meth)acrylate, hexadecyl (meth)acrylate(also known as cetyl (meth)acrylate), heptadecyl (meth)acrylate,octadecyl (meth)acrylate (also known as stearyl (meth)acrylate),nonadecyl (meth)acrylate, eicosyl (meth)acrylate and combinationsthereof. Typically, the (C₁-C₂₀)alkyl (meth)acrylate esters are(C₁-C₈)alkyl (meth)acrylate esters and preferably (C₁-C₈)alkyl acrylateesters; more preferably, the (C₁-C₈)alkyl acrylate esters are selectedfrom methyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexylacrylate; most preferably, the acrylate esters are selected from butylacrylate and 2-ethylhexyl acrylate.

[0082] With reference to aforementioned polymers (IV), (V) and (VI),suitable other copolymerizable monomers include, for example, butadiene,divinylbenzene, acrylonitrile, methacrylonitrile, crotononitrile,α-chloroacrylonitrile, ethyl vinyl ether, isopropyl vinyl ether,isobutyl vinyl ether, butyl vinyl ether, diethylene glycol vinyl ether,decyl vinyl ether, ethylene, methyl vinyl thioether and propyl vinylthioether, esters of vinyl alcohol (such as vinyl formate, vinylacetate, vinyl propionate, vinyl butyrate and vinyl versatate),poly(alkyleneoxide) di(meth)acrylates, butanediol acrylate,3-chloro-2-hydroxypropyl acrylate; amides of ethylenically unsaturated(C₃-C₆)carboxylic acids, amides of ethylenically unsaturated(C₃-C₆)carboxylic acids that are substituted at the nitrogen by one ortwo (C₁-C₄)alkyl groups, acrylamide, methacrylamide and N-methylol(meth)acrylamide; monoethylenically unsaturated monomers containingsulfonic acid or phosphonic groups (such as2-acrylamido-2-methyl-1-propanesulfonic acid,2-methacrylamido-2-methyl-1-propanesulfonic acid,3-methacryl-amido-2-hydroxypropanesulfonic acid, allyl sulfonic acid,methallyl-sulfonic acid, allyloxybenzene sulfonic acid,methallyloxybenzenesulfonic acid, 2-hydroxy-3-(2-propenyloxy)propanesulfonic acid, 2-methyl-2-propene-1-sulfonic acid, styrene sulfonicacid, vinyl sulfonic acid, 2-sulphoethyl methacrylate, 3-sulfopropylacrylate, 3-sulfopropyl methacrylate, sulfomethyl acrylamide,sulfomethyl methacrylamide and phosphoethyl methacrylate); andacetoacetoxy-containing, carboxyl-containing, vinyl-containing,amino-containing, epoxy-containing, thiol-containing andhydroxy-containing monomers not otherwise already present in the polymercomposition.

[0083] With reference to the aforementioned polymer (IV), suitablepolyvalent metal ions include, for example zinc, cadmium, nickel,zirconium, strontium, tin, calcium, magnesium and copper; preferably thepolyvalent metal ion is selected from one or more of the groupconsisting of zinc, calcium, magnesium and zirconium. When used, theamount of polyvalent metal ion and optionally a basic hydroxide or saltof an alkali metal, is from 5 to 80% of the equivalents of the acidresidues in the polymer. Suitable monovalent alkali metal ions include,for example, lithium, sodium and potassium ions. U.S. Pat. Nos.4,517,330 and 5,149,745 may be consulted for further general andspecific details on the preparation of aqueous-based emulsion polymerscross-linked with polyvalent metal ions. The optional polyvalent metalions are typically added to the aqueous medium of the coatingcomposition (pH of 4 to 8) as an aqueous slurry of the oxides,hydroxides, ammonia or polyamine complexes, and carbonates orbicarbonates of the corresponding metal ion, for example, CaCO₃, ZnO andMg(OH)₂. The polyvalent metal ions may be incorporated into the coatingcomposition at any stage of its formulation. Similarly, the basic saltof the alkaline metal may be incorporated with the polyvalent metal ionat any stage of formulating the coating composition.

[0084] With reference to the aforementioned polymer (VI), suitablepolyfunctional cross-linker agents include those containing one or morependant functional groups selected from isocyanate, carbodiimide,aziridinyl and epoxy groups. When the pendant functional group is anisocyanate group, it will react with corresponding reactive hydroxy orthiol functional groups in the first-stage polymer. When the pendantfunctional group is a carboduimide group, it will react withcorresponding carboxyl reactive functional groups in the first-stagepolymer. When the pendant functional groups are aziridinyl or epoxygroups, they will react primarily with corresponding thiol or aminoreactive functional groups in the first-stage polymer.

[0085] Suitable polyisocyanate, polycarbodiimide, polyaziridinyl andpolyepoxy cross-linker agents may be based on any aliphatic, aromatic(or mixture thereof) backbone polymer suitably substituted with thedesired pendant functional groups. For example, the backbone polymersmay be prepared by conventional vinyl polymerization or condensationpolymerization reactions where the pendant functional groups areincorporated during polymer formation or by post-reaction. Typically,the amount of polyfunctional cross-linker agent used relative to thefirst-stage polymer in preparing the aforementioned type (3) polymerswill be in an amount sufficient to provide from 0.2 to 5, preferablyfrom 0.4 to 4 and more preferably from 0.6 to 2, equivalents ofisocyanate, carbodiimide, aziridinyl or epoxy functional group, perequivalent of corresponding pendant reactive functional group in thefirst-stage polymer. Typically, this corresponds to 1 to 90%, preferablyfrom 5 to 75% and more preferably from 10 to 50%, of polyfunctionalcrosslinker, based on weight of the first-stage polymer.

[0086] When the pendant functional groups of the polyfunctionalcrosslinker agents are carboduimide, aziridinyl or epoxy groups, thebackbone polymer may be based on any suitable vinyl monomer carrying thecorresponding functional group (such as glycidyl methacrylate) orreactive group that is capable of post reacting to attach thecarbodiimide, aziridinyl or epoxy group. Alternatively, polyfunctionalcrosslinker agents based on isocyanate, carbodiumide, aziridinyl orepoxy group functionality may be derived from non-polymeric materials,as long as they are “polyfunctional” in terms of crosslinking efficacy.Suitable polyepoxide crosslinkers include, for example,(C₄-C₈)diepoxyalkanes and diepoxyaralkanes such as,1,2,3,4-diepoxybutane, 1,2,4,5-diepoxypentane, 1,2,5,6-diepoxyhexane,1,2,7,8-diepoxyoctane, 1,4- and 1,3-divinylbenzene diepoxides,(C₆-C₁₅)polyphenol polyglycidyl ethers (such as4,4′-isopropylidene-diphenol diglycidyl ether (also known as bisphenol Adiglycidyl ether) and hydroquinone diglycidyl ether), polyglycidylethers of (C₂-C₆)alkanepolyols and poly(alkylene glycols) such as,ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether,polyethyleneglycol diglycidyl ether, glycerine diglycidyl ether andtriglycidyl ether, propylene glycol diglycidyl ether and butanedioldiglycidyl ether, and polyglycidyl ethers of erythritol,trimethylolethane and trimethylol-propane.

[0087] Suitable polyaziridinyl crosslinkers include, for example,polyaziridinyl derivatives of (C₂-C₆)alkanepolyols such as,pentaerythritol-tris[β-(N-aziridinyl) -propionate],trimethylolpropane-tris[β-(N-aziridinyl)propionate],pentaerythritol-bis[β-(N-aziridinyl)propionate] andtrimethylolpropane-bis-[β-(N-aziridinyl)-propionate].

[0088] When the pendant functional groups of the polyfunctionalcross-linker agent are isocyanate groups, the cross-linkers aretypically referred to as polyisocyanates, such as the water-dispersiblepolyisocyanates and mixtures of polyisocyanates that are commerciallyavailable, for example, from Bayer Corporation (such as Bayhydur™XP-7063, XP-7148, and XP-7165 polyisocyanates), Miles Corporation orRhodia Corporation. U.S. Pat. No. 5,252,696 may be consulted for furthergeneral and specific details regarding suitable water-dispersiblehydrophilically-modified polyisocyanates that may be used as thepolyfunctional cross-linking agent. Suitable polyisocyanates include,for example, those based on derivatives of 1,4-diisocyanatobutane,1,6-diiso-cyanatohexane (HDI), 1,5-diisocyanato-2,2-dimethylpentane,2,2,4-trimethyl-1,6-diisocyanatohexane,2,4,4-trimethyl-1,6-diisocyanatohexane, 1,10-diisocyanato-decane,1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophoronediisocyanate, IPDI), 4,4′-diisocyanatodicyclohexylmethane,triisocyanates (such as 2,4,4′-triiso-cyanatodiphenyl ether,4,4′,4″-triisocyanatotriphenylmethane and trimeric1,6-diisocyanatohexane) and dimeric 1,6-diisocyanatohexane. Preferablythe polyisocyanates used as the polyfunctional cross-linker agent arebased on hydrophilically-modified derivatives of 1,6-diisocyanatohexane.Additional polyisocyanates, include, for example, those based onaromatic diusocyanates such as 2,4- and 2,6-tolylene diisocyanate,m-phenylene diisocyanate, xylylene diusocyanate, 4,4′-biphenylenediusocyanate, 1,5-naphthylene diusocyanate; preferably thepolyisocyanates used as the polyfunctional cross- linker agent aresubstantially free of aromatic isocyanate derivatives, that is, fromzero to less than 5%, more preferably from zero to less than 1% and mostpreferably from zero to less than 0.5%, based on weight ofpolyfunctional cross-linker agent.

[0089] In addition to the aforementioned (IV), (V) and (VI)acrylic-based polymer products suitable for use as base coatingcompositions, acid- functionalized polyurethane polymers may also beused. For example, the first-coating composition may be a polyurethanepolymer that is the reaction product of at least two polyol reactantsand a polyisocyanate reactant comprising as polymerized units: (a) 2 to50, preferably 5 to 15 percent, based on weight of the polyurethanepolymer, of polyol containing a carboxylic acid functional group; (b) 2to 80, preferably 30 to 70 percent, based on weight of the polyurethanepolymer, of polyol selected from one or more of saturated andunsaturated polyhydric alcohols, polyester polyols, polyether polyolsand polycarbonate polyols; (c) 20 to 70, preferably 30 to 50 percent,based on weight of the polyurethane polymer, of a polyisocyanatereactant selected from one or more of aromatic, cycloaliphatic andaliphatic polyisocyanates; and (d) zero up to 40 percent, based onweight of the polyurethane polymer, of a polyether selected from one ormore of capped polyalkyleneglycols and polyether polyols; whereincalcium ion cross-linker agent is present in an amount sufficient toprovide from 0.05 to 0.9, preferably 0.3 to 0.6, equivalents of calciumion per equivalent of corresponding carboxylic acid functional group.

[0090] Typically the acid-functionalized polyurethane polymers areprepared as pre-polymers formed from the reaction of diol compounds(such as polypropylene glycols), diisocyanate compounds (such asisophorone diisocyanate) and a polyhydroxycarboxylic acid (such as2,2-dimethylolpropionic acid) in an organic solvent in the presence of abase catalyst and further reacting the pre-polymers with chain extendingagents such as polyamines. Further examples of suitable polyols,acid-functionalized polyols and polyisocyanate reactants may be found inthe discussion of polymer (6).

[0091] Preferably, the acid-functionalized polyurethanes have from 2 to20 acid functional groups per polyurethane repeating unit. Suitablecalcium compounds useful for forming the calcium cross-links include,for example, calcium oxide, calcium hydroxide and calcium carbonate.U.S. Pat. No. 5,912,298 may be consulted for further general andspecific details on preparation of the acid-functionalized polyurethanepolymers useful as first-coating compositions.

[0092] In one embodiment of the invention, a sealer or base coatcomposition may be applied directly to a substrate and dried prior toapplication of the first-coating composition, thus providing a layerover the substrate to which the first-coating composition may bond.Suitable base coat compositions include, for example, acrylic polymerlatices having a solids content from about 2 to about 40% and preferablyfrom 4 to 25%. Preferably the acrylic polymer latices are hydrophobic innature, but may contain some hydrophilic groups. Suitable primercompositions include those commercially available from Rohm and HaasCompany (Philadelphia, Pa., USA), such as ROSHIELDT 3120 emulsion havinga polymer solids content of about 40% by weight; preferably thisemulsion concentrate is diluted with water (up to a ratio of 1 to 20parts water per 1 part emulsion) before being applied as a base coat.Although primer formulations containing the aforementioned ROSHIELD™3120 emulsion are preferred, other commercially available materials mayalso be used as base coats or sealers as described above.

[0093] Base coat formulations may be applied to a substrate by anysuitable method, for example, wiping, brushing, mopping and spraying.The latex is allowed to dry, typically under ambient conditions, and thebase coat compositions used in the present invention may then be appliedand allowed to dry and harden.

[0094] The measurement of gel fraction is used as an indication ofswellability of the polymer and its relative ease of removability understripping conditions. Uncross-linked amorphous polymers, polymers thatare lightly cross-linked, or those that have not undergone a sufficientdegree of intermolecular cross-linking will be highly solvated byappropriate solvents and therefore ‘swellable.’ Because of their reducedfree volume, polymers that have been sufficiently cross-linked in anintermolecular manner will be solubilized to a lesser extent, indicativeof decreased swellability. These less solubilized polymer molecules willbe swollen to form a soft gel which can be centrifuged out of theorganic solvent solution. Other variables, such as polymer molecularweight, polymer composition, the composition of the solvent selected,and the affinity of the polymer and solvent for each other, willinfluence the gel fraction. For polymers based on acrylic esters andstyrene as the major monomers, tetrahydrofuran (THF) is an appropriatesolvent for determining gel fraction. More hydrophilic polymers, such asthose based on moderately high levels of acidic or non-ionogenichydrophilic monomers, are more readily solvated by acetone. Othersolvents may be selected as appropriate to the composition of thepolymers to be tested, but because the polymer is added to the solventfrom an aqueous emulsion, it is preferred that the solvent be compatibleor miscible with water. U.S. Pat. No. 5,676,741 may be consulted forfurther general and specific details regarding the determination of gelfraction values for polymers.

[0095] Typically, gel fraction values may be determined by charging aweighed aliquot of solvent (W_(V)) to a weighed sample of polymeremulsion (W_(P)) of known solids content (W_(S)) into a centrifuge tube.The mixture is then stirred overnight and subjected toultracentrifugation. A weighed aliquot of the supernatant solution isthen evaporated to dryness to determine the solid fraction (S_(S)). Thesoluble fractions and gel fractions are calculated as follows:

Soluble Fraction=[S _(S)(W _(V) +W _(P) −W _(S))]/W _(S)

Gel Fraction=[1−Soluble Fraction]

[0096] One embodiment of the present invention involves coated surfacecompositions that are provided by preparing multi-layer protectivecoatings by the method of the present invention. Preferred coatedsurface compositions include, for example, substrates bearing amulti-layer coating composition where the first-coating composition isan acrylic-based polymer product comprising, as polymerized monomerunits: (a) 3 to 90 percent, based on weight of the polymer, ofmonoethylenically unsaturated monomer containing a carboxylic acidfunctional group; (b) zero up to 40 percent, based on weight of thepolymer, of a (meth)acrylic monomer containing one or more pendantreactive functional groups selected from vinyl and hydroxy groups; (c)zero up to 80 percent, based on weight of the polymer, of one or morevinyl aromatic monomers; (d) zero up to 97 percent, based on weight ofthe polymer, of one or more (C₁-C₂₀)alkyl (meth)acrylate ester monomers;(e) zero up to 10 percent, based on weight of the polymer, of one ormore other co-polymerizable monomers; and (f) zero up to 90 percent,based on equivalents of carboxylic acid groups of the polymer, ofpolyvalent metal ion. Additional preferred coated surface compositionsinclude, for example, substrates bearing a multi-layer coatingcomposition where the second-coating composition is an acrylic-basedpolymer product comprising, as polymerized monomer units: (a) zero to 30percent, based on weight of the polymer, of a monoethylenicallyunsaturated monomer containing a carboxylic acid functional group; (b) 1to 80 percent, based on weight of the polymer, of a (meth)acrylicmonomer containing functional groups selected from one or more ofisocyanurate, pendant vinyl, pendant acetoacetoxy and pendant aminogroups; (c) zero up to 70 percent, based on weight of the polymer, ofone or more viny laromatic monomers; (d) zero up to 90 percent, based onweight of the polymer, of one or more (C₁-C₂₀)alkyl (meth)acrylate estermonomers; and (e) zero up to 10 percent, based on weight of the polymer,of one or more other co-polymerizable monomers.

[0097] In a separate embodiment there is also a provided a method forapplying a highly cross-linked coating as one or more layers to asubstrate and subsequently removing all coating layers from a substratecomprising the steps of

[0098] (a) applying one or more layers of a coating comprising acurable, removable emulsion polymer;

[0099] (b) curing the composition to form a highly cross-linked coatingover the substrate by exposing the composition to ultraviolet radiation;and

[0100] (c) removing all coating layers from the substrate by exposingthe coating to one or more chemical stripping agents.

[0101] The present invention also provides a method for preparing amulti-layer coating composition comprising (a) applying a first-coatingcomposition to a substrate wherein the first-coating compositioncomprises a polymer product having a gel fraction of 0.3 to 0.95 in asolvent selected from one or more of acetone and tetrahydrofuran andwherein the first-coating composition is applied in one or more separateapplications, allowing the first-coating composition to dry after eachapplication; and (b) applying one or more layers of a coating comprisinga curable, removable emulsion polymer.

[0102] The method of the present invention may be illustrated by thefollowing description. A substrate is coated with a base coat that isreadily removable under conventional stripping conditions, where thefirst-coating composition has a gel fraction value in organic solvent of0.30 to 0.95. The base coat is typically applied in a single step andallowed to dry; optionally the base coating may be applied in multiplesteps where each application is allowed to dry before the nextapplication; in the case of multiple applications, 2 to 5 separateapplications are typically used, followed by a final drying step toallow the base coating to harden. The coating compositions useful in thepresent invention readily dry at temperatures as low as 10° C. For thepurposes of the present invention, “allowed to dry” (as in ‘eachapplication is allowed to dry before the next application’) refers tothe coating composition drying and hardening to the point where thesurface is no longer soft or tacky to the touch under light fingerpressure.

[0103] After the base coating has been applied onto a surface, aremovable, UV curable coating is applied over and onto the dried basecoat composition. The top coat composition has a gel fraction value inorganic solvent of greater than 0.95 and up to 0.99. Similarly to thatdescribed above for application of the base coating composition, theremovable UV curable composition may be applied in one or more separateapplications where each application is allowed to dry before the nextapplication, followed by a final drying step to allow the top coatingcomposition to dry and harden. In one embodiment the top compositionitself is highly durable and removable under conventional strippingconditions. In another embodiment the top composition itself is highlydurable and resistant to removal under conventional stripping conditions(‘non-removable’) if it were to be applied directly to a hard surfacesubstrate, or optionally over a primer or sealer layer applied to thesubstrate. However, the resultant multi-layer coating compositions ofthe present invention, comprising the second-coating composition appliedonto the first-coating composition, provide enhanced durability anddetergent resistance, yet are readily removable under conventionalstripping conditions.

[0104] Some embodiments of the invention are described in detail in thefollowing Examples. All ratios, parts and percentages are expressed byweight and all reagents used are of good commercial quality unlessotherwise specified. Abbreviations used in the Examples and Tables arelisted below with the corresponding descriptions: BA = butyl acrylateMMA = methyl methacrylate GMA = glycidyl methacrylate AA = acrylic acidMAA = methacrylic acid HEMA = hydroxyethyl methacrylate ST = styreneBHMR = black heel mark resistance (% coverage) [NCO] = isocyanateconcentration [equivalents] [OH] = hydroxyl or hydoxy groupconcentration [equivalents]

[0105] Test Methods

[0106] Mar Resistance: This test is based on striking the coating at ashallow angle with a hard object; in the examples provided, the objectwas the fingernail of the individual performing the test. This testgives an indication of how the coating will resist marring, which leadsto gloss reduction of the coating.

[0107] After the coating is applied to the substrate and allowed tocure, the coated substrate is placed on a solid surface such as a tabletop and struck with the operator's fingernail. The operator's fingernailis kept parallel to the coated surface and the impact angle is greaterthan 45° from the normal of the surface, to increase the likelihood ofmarking the coating.

[0108] When comparing coatings, it was important that the same operatorperform the test. This test was designed to distinguish relativedifferences.

[0109] The following rating system was used: Rating Appearance 1 -Excellent (Exc) No perceptible marks 3 - Good Marks which appear as thinscratches (<1 mm) 5 - Poor Marks which are wide (>1 mm)

[0110] Black Heel Mark Resistance (BHMR): The method for determiningblack heel described in Chemical Specialty Manufacturers AssociationBulletin No. 9-73 was utilized, except that commercially availablerubber shoe heels were used in place of the recommended 5.08 cm (2 inch)rubber cubes. Furthermore, instead of subjectively rating the coatedsubstrate, the percentage of the coated substrate area covered by blackheel marks was determined; this was conveniently performed withtransparent graph paper. A black heel mark is an actual deposition ofrubber onto or into the coating.

[0111] Detergent Resistance: The method for determining detergentresistance is described in “Annual Book of ASTM Standards,” Section 15,Volume 15.04, Test Procedure ASTM D 3207 (2000), except that a {fraction(1/20)} dilution of Forward™ (S.C. Johnson and Sons, Inc., Racine, Wis.)in water was used as test detergent solution and a 1000-g weight wasadded to the brush assembly.

[0112] Removability: The method for determining polish removability isdescribed in “Annual Book of ASTM Standards,” Section 15, Volume 15.04,Test Procedure ASTM D-1792 (2000), except that a 1000-g weight was addedto the boat assembly and a 1:2 aqueous mixture (1 part commercialstripper solution/2 parts water) of commercial stripper solution (5-15%2-butoxyethanol and 30-40% monoethanolamine in water, provided as“FloorStar Power Strip” from ServiceMaster Company, Downers Grove, Ill.)was used as the stripping solution. Additionally, a commercial strippingsolution of 5-15% 2-butoxyethanol and 30-40% monoethanolamine in waterwas further diluted with warm water (130-150° F.) and allowed to resideon the coated panel for 10 minutes before starting the scrub cycle.

[0113] Coating Application and Testing: The method for applying thefloor polish (base coat or top coat) to substrates for testing purposesis described in “Annual Book of ASTM Standards,” Section 15, Volume15.04, Test Procedure ASTM D 1436 (2000). Test Method B (application ofemulsion floor polish with a hand applicator) was used.

[0114] Preparation of multi-layer coatings: two coats of base coatpolymer polish followed by two coats of top coat polymer were applied tovinyl composition panels with about one hour between coats. After thefinal coat, the coated panels were allowed to cure at 25° C. for 24hours before testing. This format was used to evaluate mar, black heelmark and detergent resistance as well as polish film removability.

[0115] The following abbreviations and terms are used as indicators ofposition on scales of ratings used in reporting the “detergentresistance” and “ease of removability” characteristics, where “VeryPoor” is the lowest rating and “Excellent” the highest rating: VP = VeryPoor P = Poor F = Fair G = Good VG = Very Good Exc = Excellent

[0116] Formulation of Base Coat (First-Coating) Composition

[0117] The base coat floor polish was formulated by combining thevarious components listed below in Table 1 in the order indicated. Thebase coat polymer used to prepare samples of the multi-layer coatingcompositions of the present invention is described in Example 1.

EXAMPLE 1

[0118] Emulsion polymer having a composition of 30 BA/10.5 MMA/5HEMA/4.5 MAA//40 ST/5 MMA/5 AA prepared as described in U.S. Pat. No.4,150,005. The polymer emulsion further contained 40 equivalent % Zn⁺⁺(added as zinc ammonium bicarbonate). The pH of the emulsion wasadjusted to 9.0 with a final polymer solids content of 38%. TABLE 1 BaseCoat Floor Polish (see order of addition below) Amount Material Function(parts by weight) Water diluent 31.57 Zonyl ™ FSJ (1%)¹ wetting agent0.50 Kathon ™ CG/ICP (1.5%)² biocide 0.03 SE-21³ defoamer 0.02Diethylene Glycol Ethyl coalescent 2.04 Ether Dipropylene Glycolcoalescent 2.04 Methyl Ether Dibutyl Phthalate plasticizer 0.93Tributoxy Ethyl leveling aid 0.93 Phosphate Polymer Emulsion vehicle45.68 (Example 1) Michem Dispersion alkali-soluble resin 3.86 MD-915(30%)⁴ AC-392N (35%)⁵ aqueous polyethylene 6.41 wax emulsion EpoleneE-43N (40%)⁶ aqueous polyethylene 5.79 wax emulsion

[0119] Formulation of Top Coat (Second-Coating) Composition 1

[0120] A top coat floor polish was formulated by combining the variouscomponents listed below in Table 2 in the order indicated. The top coatpolymer used to prepare this floor polish formulation is described inExample 2.

EXAMPLE 2

[0121] Emulsion polymer having a composition of 53 MMA/34 BA/10 HEMA/3MAA (pH=7.5, final polymer solids of 41%) with an [OH] equivalent weightof 3100, based on the HEMA content of the emulsion polymer, was used asthe Part A polymer emulsion component in Table 2.

EXAMPLE 2A

[0122] Water-dispersible polyisocyanate based on diusocyanatederivatives is available as Bayhydur™ XP-7063 polyisocyanate (100%active ingredient, 17.1% [NCO], 245 g/equivalent [NCO]) from BayerCorporation, Pittsburgh, Pa., and was used as component B in Table 2.

[0123] The top coat formulation was prepared by slowly adding Part B toPart A, followed by mild agitation for 5-10 minutes, to provide a finaltop coat polish formulation having 33.6% solids with an [NCO]:[OH]stoichiometric ratio of 1.1:1. TABLE 2 Top Coat Floor Polish 1 (seeorder of addition below) Amount Material Function (parts by weight) PartA: Polymer Emulsion acrylic emulsion 62.95 (Example 2) Premix and addunder 0.50 agitation: Water diluent 25.23 Dipropylene Glycol solvent1.89 Monomethyl Ether (DPM) Then add: Byk 346¹ flow Aid 0.09 Acrysol ™RM-825² rheology modifier 0.19 Tego Glyde ™ 410³ mar aid 0.19 (50% inDPM) Tego Foamex ™ 805³ defoamer 0.94 Surfynol ™ 104DPM⁴ wetting aid0.47 Part B: Bayhydur ™ XP-7063 polyisocyanate 5.50

[0124] Formulation of Top Coat (Second-Coating) Composition 2

[0125] A radiation-curable top coat floor polish was formulated bycombining the various components listed below in Table 3 in the orderindicated. The top coat polymer used to prepare this floor polishformulation is described in Example 3.

EXAMPLE 3

[0126] Emulsion polymer having a composition of 37 BA/20 MMA/24 GMA/19ST (typical pH=7.1, final polymer solids of 40-41%) was used as thepolymer emulsion component in Table 3.

[0127] The top coat formulation was prepared by mixing the ingredientsas listed in Table 3 to provide a final top coat polish formulationhaving 38% solids with a pH of 6.8.

[0128] The top coat formulation 2 was applied to panels as describedunder “Coating Application and Testing” section, allowed to dry andstored approximately 30 minutes at ambient temperature followed bycuring in a UV apparatus. The curing system was Fusion UV-System, HP-6series, with an H bulb, rated at 197 W (watts)/cm. The panels werepassed under the UV light six times at a speed of 22 cm/second (44feet/minute). The dosage was adjusted to 630 mJ/cm² per pass. Thesamples were passed through the focal plane of the lamp. TABLE 3 TopCoat Floor Polish 2 (see order of addition below) Amount MaterialFunction (parts by weight) Polymer Emulsion acrylic emulsion 92.4(Example 3) Add under agitation: Darocur ™ 1173¹ photoinitiator 0.55Water diluent 5.38 Tego Glyde ™ 410² mar aid 0.23 (50% in DPM)Surfynol ™ 104DPM³ wetting aid 0.54 Acrysol ™ RM-825⁴ rheology modifier0.70 Byk 346⁵ flow aid 0.09

[0129] Experimental Test Results

[0130] Testing of coating compositions represented by Examples 4-8demonstrates the improvement in performance properties of coatingformulations using the multi-layer coating compositions of the presentinvention.

EXAMPLE 4

[0131] (comparative)

[0132] Coating composition coated onto test panel using coatingformulation described in Table 1 (base coat alone).

EXAMPLE 5

[0133] (comparative)

[0134] Coating composition coated onto test panel using coatingformulation described in Table 2 (top coat floor polish 1 alone).

EXAMPLE 6

[0135] (present invention)

[0136] Multi-layer coating composition coated onto test panel using basecoat formulation described in Table 1 and top coat formulation 1described in Table 2, applied as described under “Coating Applicationand Testing” section.

EXAMPLE 7

[0137] (comparative)

[0138] Coating composition coated onto test panel using coatingformulation described in Table 3 (top coat floor polish 2 alone).

EXAMPLE 8

[0139] (present invention)

[0140] Multi-layer coating composition coated onto test panel using basecoat formulation described in Table 1 and top coat formulation 2described in Table 3, applied as described under “Coating Applicationand Testing” section.

[0141] Tables 4 and 5 summarize the performance properties of themulti-layer coating compositions of the present invention with regard todurability and ease of removability. Multi-layer coating compositions ofthe present invention, represented by Examples 6 and 8, combine thedurability benefits (mar, black heel mark and detergent resistance) ofthe individual top coat compositions (Examples 5 and 7) with the ease ofremovability of the base coat composition (Example 4), but without thepoor removability of the individual top coat compositions or the poordurability of the base coat composition when used alone. TABLE 4 Ex 4*Ex 5* Ex 6 Base Coat Yes No Yes Top Coat No Yes Yes Mar Resistance 3 1 1BHMR (% Coverage) 5.7 2.1 1.9 Detergent Resistance Good Exc ExcRemovability Exc Poor Good

[0142] TABLE 5 Ex 4* Ex 7* Ex 8 Base Coat Yes No Yes Top Coat No Yes YesMar Resistance 3 1 1 BHMR (% Coverage) 5.7 2 2 Detergent Resistance GoodExc Exc Removability Exc Poor Good

We claim:
 1. A coating composition comprising a multi-stage emulsionpolymer that is both radiation curable and removable and includeschemically reactive functional groups in the coating that react with oneor more chemical stripping agents, effecting the removal of the coatingfrom a substrate.
 2. The coating of claim 1 wherein the multi-stageemulsion polymer comprises, as polymerized monomer units (a) zero to 60percent, based on weight of the polymer, of a mono-ethylenicallyunsaturated monomer containing a carboxylic acid functional group; (b) 1to 80 percent, based on weight of the polymer, of a (meth)acrylicmonomer containing functional groups selected from one or moremonoethylenically unsaturated monoepoxides, glycidyl (meth)acrylate,allyl glycidyl ether, glycidyl cinnamates, glycidyl crotonates, glycidylitaconates, glycidyl norbornenyl ester, glycidyl norbornenyl ether andother acrylate containing pendant vinyl groups; (c) 20 to 80 percent,based on weight of the polymer, of one or more (C₁-C₂₀)alkyl(meth)acrylate ester monomers; and (e) zero to 10 percent, based onweight of the polymer, of one or more other co-polymerizable monomers.3. The coating of claim 1 wherein the UV curable, removable compositionis included within one or more layers applied on top of a substrate. 4.The coating of claim 1 wherein the UV curable, removable composition isincluded within one or more layers applied on top of a base coat, thebase coat disposed on top of a substrate.
 5. The coating of claim 3 orclaim 4 wherein the substrate refers to any surface that is vertical,horizontal or inclined upon which the coating is applied and is selectedfrom the group consisting of flooring, wall, ceiling, tile materials,vinyl floor tiles, tiles coated with sealer or primer, ceramic tiles,wood, metal, concrete, marble, slate and simulated natural stone.
 6. Amethod for applying a UV cured, highly cross-linked coating as one ormore layers to a substrate and subsequently removing all coating layersfrom a substrate comprising the steps of: (a) applying one or morelayers of a coating comprising a curable, removable multi-stage emulsionpolymer; (b) curing the composition to form a highly cross-linkedcoating over the substrate by exposing the composition to ultravioletradiation; and (c) removing all coating layers from the substrate byexposing the coating to one or more chemical stripping agents.
 7. Themethod according to claim 6 wherein the curable, removable multi-stageemulsion polymer comprises, as polymerized monomer units (a) zero to 60percent, based on weight of the polymer, of a mono-ethylenicallyunsaturated monomer containing a carboxylic acid functional group; (b) 1to 80 percent, based on weight of the polymer, of a (meth)acrylicmonomer containing functional groups selected from one or moremonoethylenically unsaturated monoepoxides, glycidyl (meth)acrylate,allyl glycidyl ether, glycidyl cinnamates, glycidyl crotonates, glycidylitaconates, glycidyl norbornenyl ester, glycidyl norbornenyl ether andother acrylate containing pendant vinyl groups; (c) 20 to 80 percent,based on weight of the polymer, of one or more (C₁-C₂₀)alkyl(meth)acrylate ester monomers; and (e) zero to 10 percent, based onweight of the polymer, of one or more other co-polymerizable monomers.8. A method for preparing a UW curable and removable multi-layer coatingcomprising (a) applying one or more layers of a base coat to a substratewherein the base coat comprises a polymer product having a gel fractionof 0.3 to 0.95 in a solvent selected from one or more of acetone andtetrahydrofuran and wherein the base coat is applied in one or moreseparate applications, allowing the base to dry after each application;and (b) applying one or more layers of a coating comprising a curable,removable multi-stage emulsion polymer.
 9. The method according to claim8 wherein the curable, removable multi-stage emulsion polymer comprises,as polymerized monomer units (a) zero to 60 percent, based on weight ofthe polymer, of a mono-ethylenically unsaturated monomer containing acarboxylic acid functional group; (b) 1 to 80 percent, based on weightof the polymer, of a (meth)acrylic monomer containing functional groupsselected from one or more monoethylenically unsaturated monoepoxides,glycidyl (meth)acrylate, allyl glycidyl ether, glycidyl cinnamates,glycidyl crotonates, glycidyl itaconates, glycidyl norbornenyl ester,glycidyl norbornenyl ether and other acrylate containing pendant vinylgroups; (c) 20 to 80 percent, based on weight of the polymer, of one ormore (C₁-C₂₀)alkyl (meth)acrylate ester monomers; and (e) zero to 10percent, based on weight of the polymer, of one or more otherco-polymerizable monomers.
 10. The method according to claim 8 or claim9 wherein the substrate refers to any surface that is vertical,horizontal or inclined upon which the coating is applied and is selectedfrom the group consisting of flooring, wall, ceiling, tile materials,vinyl floor tiles, tiles coated with sealer or primer, ceramic tiles,wood, metal, concrete, marble, slate and simulated natural stone.